This invention relates to a method and apparatus for regulating the fat content of milk, of the type wherein whole milk is separated into a nonfat component and a fatty component, and part of the fatty component is then re-added to the nonfat component to form a mixture.
An article entitled "Milchstandardisierung: Herstellung von Milch mit einem bestimmten Fettgehalt," by H. Niemeyer, in Deutsche Milchwirtschaft 26(8) of 19 Feb. 1975, describes various methods of producing milk having a specific fat content. In most of the known methods, the raw product, i.e., the whole milk, is separated in a separator into a nonfat component and a fatty component, e.g., skim milk and cream. These two components are stored in separate tanks, and after determination of the fat content of the whole milk and of the fatty component obtained by means of the separator, a predetermined amount of either the fatty or the nonfat component is mixed into whole milk, making the end product, i.e., the so-called standardized milk, lower or richer in fat.
Another method is to separate the whole milk in a separator into a nonfat and a fatty component, roughly adjusting the fat content of the fatty component to any desired value by inserting volume limiters. After the separator, part of the fatty component is first re-added to the nonfat component according to the desired fat content of the end product. The rest of the fatty component is led off and stored in a separate tank. The mixture having a roughly adjusted fat content is likewise stored in another tank. After determination of the fat content of the mixture, of the raw product, and of the fatty component, the fat content of the end product, i.e., of the standardized milk, is corrected by addition of either nonfat or fatty component.
The drawback of these two known methods is that an extensive tank installation is needed, that processing is relatively time-consuming, and that a long delay is unavoidable between reception of the whole milk and processing, i.e., production of the standardized milk. The fat content of the whole milk, or the nonfat and fatty components, and of the standardized milk is determined by taking samples which are tested for their fat content in a laboratory.
Fully-automatic adjustment of the fat content of milk has also already been proposed. According to one fully-automatic method, after the whole milk has been separated into a nonfat and a fatty component, the density of the nonfat component, which density is dependent upon the fat content, is measured by means of a hydrometer. According to the result of this determination of the fat content, a dosing member is triggered via a computer and supplies to the nonfat component an amount of the fatty component corresponding to the desired fat content of the end product. In this method, the fat content of the resultant product is not measured directly. Inasmuch as density is dependent upon temperature, temperature fluctuations bring about wide variations in the measured fat content even though there is no significant change in the actual fat content.
In another known fully-automatic method, the fat content of the standardized milk is determined by means of a special measuring device. First the whole milk is separated in a separator into skim milk and cream, and then part of the cream is re-added to the skim milk via a dosing member. After mixing, a sample is automatically withdrawn every half-minute, the fat content of this sample is automatically determined with the aid of the special measuring device, and the dosing member is readjusted according to the result of this measurement. The fat content is determined according to the principle of light-dispersion measurement by a very sensitive measuring element which is exposed to the rather rough conditions of normal dairy operation and is often damaged. Measurement does not take place continuously but at intervals, so that incorrect adjustment is quite possible during the intervals. Moreover, the measuring device must be frequently recalibrated if the fat content of the standardized milk is not to vary too much from the specified norm. Finally, the cleaning of this measuring device entails certain problems, and readjustment is necessary after cleaning.